1. Field of the Invention
This invention relates to an unexpected improvement found in the physical properties of glass-reinforced polyglutarimides when a low level of phenoxy resin is incorporated into the blend.
There exists a need for high softening (high glass temperature) glass-reinforced amorphous resins which also possess high modulus values (imparted by the glass) and acceptable impact strength for the various uses to which such resins might be put, such as in the electronics industry, where resistance to heat during assemblage and soldering is necessary, plus load-bearing capacity and ability to resist breakage on handling. Polyglutarimides, when glass-reinforced, have attractive properties for such a market, but additional toughness without the excessive loss in physical properties imparted by conventional impact modifiers is desirable. A solution to improvement of impact without loss in modulus properties and with only small decrease in softening temperature has been found with the addition of low levels of phenoxy resin to the polyglutarimide//glass combination.
2. Description of the Prior Art
Polyglutarimides, otherwise known as polymethacrylimides, are polymers which contain the unit ##STR1## wherein R.sup.1 and R.sup.2 may be the same or different and are hydrogen or lower alkyl of up to four carbon atoms, such as methyl, ethyl, or butyl, and R.sup.3 is H or alkyl, such as methyl, butyl, dodecyl, and the like. The polyglutarimides best known to the art are those where R.sup.1 and R.sup.2 are methyl and R.sup.3 is hydrogen, methyl, other lower alkyl, or cyclohexyl. Particularly preferred are those polymers derived from poly(methyl methacrylate) and monomethylamine, where R.sup.1 =R.sup.2 =R.sup.3 =methyl.
Kopchik, U.S. Pat. No. 4,246,374 has described an efficient method for the production of such polyglutarimides in a continuous reactive extrusion process, although other methods, such as solution imidization, are known to the art. The Kopchik process, as well as all others known to the art, produce some residual acid and anhydride groups in the polyglutarimide if the extent of imidization is below about 95 percent of theoretical. Hallden-Abberton et al., U.S. Pat. Nos. 4,727,117 and 5,004,777, describe an acid-reducing or "capping" process for esterification or alkylation of such acid and anhydride groups to replace them by ester groups. These patents further describe the effect on compatibility with various resins between the "capped" and "uncapped" polyglutarimides.
Kopchik has described that polyglutarimides exhibit good acceptance of glass fiber reinforcement; such acceptance is maintained by the acid-reduced polymers of Hallden-Abberton.
Hallden-Abberton has published an extensive list of polymers which may be blended with the acid-reduced polyglutarimide, and has exemplified, among many others, a 50/50 blend with a phenoxy resin having a single glass temperature, indicative of compatibility, and being translucent in appearance.
The prior art reports blends of certain engineering resins, such as poly(butylene terephthalate), exhibit improved properties when the glass fiber surface is pre-coated with a phenoxy resin prior to blending.
There is no teaching or suggestion in the prior art that low levels of a specific resin (phenoxy resin) would be effective in raising the physical properties of glass-reinforced aliphatic polyglutarimides, especially when all organic components are directly compounded together in a single blend prior to addition of the glass fiber.